Effective therapeutic targets interact with pathogenic pathways across multiple levels of vascular physiology. We propose that AMP-activated kinase (AMPK) serves such a role in the lung and thus has the capacity to become a novel drug target in the treatment of PH. Our data indicate AMPK dysfunction contributes to the pathogenesis of PH in proximal vessels and distal vessels through distinct signaling mechanisms. Specifically, that attenuated AMPK expression and activity promotes vascular remodeling induced by smooth muscle proliferation in large vessels and disordered endothelium in capillaries. Resolving AMPK function in PH will provide new understanding of signaling specificity and molecular targeting at multiple points in this disease process. Utilizing state of the art methods in molecular biology and cell isolation, we find that in cells derived from the main truncus, i.e. pulmonary artery endothelial and smooth muscle cells, AMPK inhibition caused an increase in cell growth that was dependent on the culture environment. In contrast, endothelial cells obtained from distal (<150?m diameter) vessels, i.e. pulmonary microvascular endothelial cells, failed to grow in the presence of AMPK inhibition. Interestingly, AMPK activation had no effect on cellular proliferation or growth of any cell type indicating it was loss of AMPK activity that contributed t abnormal cell growth. These in vitro data were confirmed in vivo by histological approaches using rat and human lung, which revealed that in regions of abnormal vasculature in the PH lung--where increased medial hypertrophy or the presence of plexiform lesions were noted--a marked decrease or complete absence of AMPK staining was observed linking loss of AMPK to location specific disease progression. Moreover, AMPK subunits were detected in lung lavage fluid and blood. This finding in combination with preliminary data indicating that AMPK subunit expression patterns are altered in PH suggests AMPK has potential application as a biomarker of PH vascular disease. This proposal tests the overall HYPOTHESIS: that impaired AMPK activity contributes to vascular pathogenesis associated with PH. SPECIFIC AIMS test the HYPOTHESES that: [1] Impaired AMPK activity contributes to the pathogenesis of PH in proximal and distal vessels through distinct isoform dependent signaling mechanisms. 2] Changes in AMPK ????? expression patterns correlate with segment specific vascular disease in PH.